1. Field of the Invention
This invention relates to surgical trocars. More particularly, this invention relates to an improved trocar having an extremely sharp tip for making incisions.
2. State of the Art
Laparoscopic surgery is widely practiced throughout the world today and its acceptance is growing rapidly. In general, laparoscopic surgery involves creating an entry port into the body of a patient by forcing a trocar carrying a trocar tube through the abdominal wall, removing the trocar and leaving the trocar tube in place. Laparoscopic tools may be inserted through the trocar tube in order to perform minimally invasive surgery or diagnostic procedures. The trocar assembly generally includes a trocar having a sharp distal tip, and a proximal housing which carries a trocar tube which surrounds the trocar and includes a sealing or valve member associated with the trocar tube. In the assembled position ready for use, the sharp tip protrudes from the distal end of the trocar tube. The trocar is inserted into the body by pressing the trocar against the patient's skin, causing the trocar tip to make an incision in the skin so that the trocar tube can penetrate the body. After penetration, the trocar is removed from the trocar tube and valve housing, leaving the valve housing exterior of the body with the trocar tube extending into the peritoneal cavity. Surgical viewing endoscopes, cameras, lenses, or other viewing instrumentation are then inserted through the trocar tube while a cutter, dissector, or other surgical instrument is inserted through another trocar tube for the purpose of manipulating and/or cutting the internal organ or tissue. It is often desirable to have several trocar tubes in place at once in order to receive several surgical instruments. In this manner, organs or tissue may be grasped with one surgical instrument, and simultaneously may be cut with another surgical instrument; all under view of the surgeon via the viewing instrumentation in place.
It is desirable for the trocar to make the smallest and least disfiguring incision possible. To this end, an extremely sharp trocar tip is preferred which requires the least amount of pushing pressure and makes a clean incision. A well known trocar tip design includes a solid cylindrical body with multiple bevels at the distal end forming a three faced pyramidal point. The pyramidal point is provided by feeding a solid aluminum or stainless steel rod through an automatic grinding machine which grinds a flat on the end of the rod at an angle of 17.degree. to the longitudinal axis of the rod. The grinding machine rotates the rod 120.degree. about its longitudinal axis and grinds a second 17.degree. flat, and then rotates the rod another 120.degree. about its longitudinal axis and grinds the third 17.degree. flat. This known design, however, requires a relatively large force to thrust the trocar into the abdomen. In addition, the incisions made by these designs often result in excessive tearing of the skin because the beveled surfaces of the pyramidal tip tend to push the skin apart before it is cut. This is because the actual cutting edges are formed by 68.degree. intersections of adjacent flats, whereas the optimal cutting edge for a durable knife is a 22.degree. intersection of flats. Nevertheless, the 68.degree. cutting edges of the three faced pyramidal tip are the sharpest possible edges for that configuration. If the grinding angle of 17.degree. is increased or decreased, the cutting edge angle of 68.degree. will increase according to the trigonometry of tetrahedrons.
Other trocar tip designs exist providing certain advantages over the well known pyramidal tip. U.S. Pat. No. 4,601,710 to Moll discloses a trocar assembly including a trocar having a distally biased hollow frustroconical safety shield with three radial slots. The sharp point of the trocar includes three radially arranged blades each of which has a leading cutting edge and two trailing edges forming a double beveled blade edge which is angled proximally from the tip. When the frustroconical safety shield is pressed proximally against its biasing spring, the three slots in the safety shield permit exposure of the three blades. Moll's trocar design provides a sharp cutting tip and avoids the beveled surfaces of the pyramidal tip which tend to tear and scar the skin at the entry point of the trocar. However, the three blade tip taught by Moll is expensive to make because six surfaces must be ground, and the resulting trocar is still is not as sharp as desirable.